1. Field of the Invention
The present invention relates to a cosmetic or dermatological composition comprising an emulsion of oil-in-water type. It more particularly relates to a composition comprising an oil-in-water emulsion formed by oily globules which are provided with a lamellar liquid crystal coating and are dispersed in an aqueous phase. The invention also relates to a process for the preparation of such a composition and its application to the treatment of skin and keratinous matter.
2. DIiscussion of the Background
Numerous lipophilic active compounds have an important role to play within the field of skin care. Examples of such active agents which may be mentioned are the lipophilic vitamins A, E or F, the essential oils, sunscreen agents, long-chain alkyl esters of .alpha.-hydroxy acids, anti-inflammatory agents and agents stimulating the biosynthesis of lipids and/or of proteins.
Their use is very widespread but their effectiveness is limited by their lipophilic nature. They are, in fact, only partially absorbed by the skin and diffuse only with great difficulty into the stem cells of the stratum corneum, in which cells they are stopped by the presence of aqueous compartments in the intercorneocytic spaces.
Their introduction into oil-in-water emulsions stabilized by a monolayer of surfactants hardly improves this state of affairs, given that these emulsions are broken as soon as they are applied to the skin, releasing at the surface of the skin an oily phase containing lipophilic active agents which are very poorly absorbed for the reasons stated above.
Attempts to improve this state of affairs have been proposed in the prior art.
In JSCC 35, 45-57 (January, February 1984), Junginger et al. describe oil-in-water emulsions whose stabilization is provided by a lamellar liquid crystal three-dimensional network.
In "Secondary droplet emulsion: Contribution of liquid crystal formation to physicochemical properties and skin moisturizing effect of cosmetic emulsion" (12th International Congress IFSSC, Paris September 1992, Abstracts, Vol. I, 117-136), Suzuki et al. describe these oil-in-water emulsions as forming superstructures ("secondary droplets"), aggregates of oily droplets coated with liquid crystal lamellae. These authors show that the existence of these superstructures is dependent on the presence of fatty alcohol.
The main qualities of this type of emulsion are stability with respect to the release of oil and a skin moisturizing effect. However, this type of emulsion has disadvantages. It is, in fact, necessary to use large amounts of surfactant in order to constitute the three-dimensional network, thereby increasing the risks of intolerance on the part of the user, which is reflected in a long "soaping" (persistence of a white color) during the application of such compositions to the skin. In addition, the oil dispersion is coarse and heterogeneous, and the oil is more sequestered by the three-dimensional network than genuinely dispersed in the form of individualized oil microdroplets. The oil droplets generated by this type of emulsion have a mean size which is very much greater than the intercorneocytic spaces that they have to cross and very much greater than the hair pores into which they have to be taken up, which contributes towards explaining the very partial penetration into skin and hair of the fatty phase and of the active agents which are dissolved therein.
Also known is the article by Dahms in Cosmetics and Toiletries, Vol. 101 November 1986, which describes emulsions having the same characteristics and, thus, the same drawbacks.
It is thus observed that the need still remained in the prior art for emulsions allowing an improved penetration of cosmetic or dermatological compositions into the skin and hair.
The Applicant has now discovered a new emulsion which allows this objective to be achieved.